ML20070E596
| ML20070E596 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/08/1994 |
| From: | Powers K TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9407150208 | |
| Download: ML20070E596 (4) | |
Text
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A Twww.e VWg A#eny, TM On% Gu IOR 6:XMrDaGy h nrew e 37379 MfjQ Ken Powers wi.rn, m,t unma uxw na n
July 8, 1994 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:
In the Matter of
)
Docket No. 50-327 Tennessee Valley Authority
)
SEQUOYAH NUCLEAR PLANT (SQN) - REQUEST FOR DISCRETIONARY ENFORCEMENT FOR UNIT 1 TECHNICAL SPECIFICATION (TS) 3.8.1.1, ACTION a FOR DIESEL GENERATOR (D/G) 2A-A This letter serves to document TVA's request for discretionary enforcement for Unit 1 TS 3.8.1.1, Action a, for D/G 2A-A.
During a modification to replace the electric governor for the 2A-A D/G, problems were encountered with the modification and with the subsequent postmodification testing. As a result, the 72-hour allowed outage time provided in TS 3.8.1.1, Action a, is anticipated to be exceeded by approximately 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br />. Compensatory actions are being taken as described in the enclosed discretionary enforcement request. This request has been PORC approved.
In order to allow adequate time to complete the testing of the 2A-A D/G, 41 hours4.74537e-4 days <br />0.0114 hours <br />6.779101e-5 weeks <br />1.56005e-5 months <br /> is being requested in addition to the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided by TS 3.8.1.1.
Without this additional time Unit 1 will begin a shutdown as l
required by TSs at 1954 Eastern daylight time on July 8, 1994.
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U.S. Nuclear Regulatory Commission Page 2 July 8, 1994 i
Please direct questions concerning this issue to J. D. Smith at (615) 843-6672.
Sincerely bj Y
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Ken Powers i
Enclosure cc (Enclosure):
Mr. D. E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administrator l
U.S. Nuclear Regulatory Commission Region Il 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323-2711 t
i
a One train of auxiliary building gas treatment system Vital Battery Exhaust Fan I These support systems are necessary to support Unit 1 operation in the event of a loss-of-offsite power. There is no impact if the offsite power remains available.
In the event of a loss-of-offsite power, the redundant train capability is available for all of the affected functions.
In addition, emergency capability is provided in the design to cross train the essential raw cooling water headers and the shutdown board electrical distribution centers. Since the affected functions are support functions, immediate availability is not necessarily required to mitigate design basis events. Sufficient time is considered available to establish and implement appropriate controls to effectively utilize the available cross ties under extreme conditions (loss-of-offsite power, design basis l
events, and failures of the other emergency power trains or equipment).
Compensatory actions have been taken in accordance with the defense in depth approach at SQN to protect the switchyard and the opposite train of equipment.
In addition, the grid is stable in operation.
In support of the efforts, TVA has performed a probabilistic safety assessment (PSA) to determine the core damage frequency (CDF) for a postulated loss-of-coolant accident concurrent with a loss-of-offsite power, one of four D/Gs unable to automatically load, and assuming an additional failure occurring in any one of the three remaining 6.9-kilovolt shutdown boards during the additional time period requested.
The probability of core damage assuming an additional failure during the current TS period of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is 9.89E-7 versus 1.55E-6 for a TS period of 113 hours0.00131 days <br />0.0314 hours <br />1.868386e-4 weeks <br />4.29965e-5 months <br />.
The additional A0T to TS 3.8.1.1 has been determined to be of limited safety significance.
In addition, the risk associated with shutting Unit i down is judged to be greater than the risk associated with the addition unavailability time for D/G 2A-A.
These risks include the power system transfer associated with the unit shutdown; the complete reliance on electric power for decay heat removal in Mode 5; and the additional management challenges associated with shutting the unit down.
Accordingly, the requested waiver will not result in a significant increase in the probability or consequences of a previously evaluated accident, will not create the possibility of a new accident, and will not result in a significant reduction in the margin of safety. Also, the action does not involve an unreviewed environmental question because it does not increase any adverse environmental impacts, change effluents or power levels, or result in unreviewed environmental matters.
ENCLOSURE Discretionary Enforcement for Technical Specification (TS) 3.8.1.1 Because of Diesel Generator (D/G) Governor Modification Complications
Background
Sequoyah has elected to upgrade the D/G electric governor to Model 2301A during the Unit 2 Cycle 6 outage.
The new model governor is less susceptible to electro-motive force (EMF) noise, has an improved transient response, and creates better separation between the electrical t
and mechanical governors.
In the past, Sequoyah has experienced EMF interference in Electric Governor 2301 that has caused unplanned unavailability.
This modification is similar to actions taken at other utilities.
Lessons learned at these utilities have been factored into the modification at SQN. Also, a vendor representative has been made available for resolution of problems as they occur.
In addition, coordination between Nuclear Engineering, Systems, Modifications, and Operations has been well staged.
It should be noted that delays have been encountered at other utilities during the modification. However, unit separation of the D/Gs at these utilities allow the modification to occur without entering the limiting condition of operation (LCO) action.
Even with the application of those lessons learned and pre-job coordination, delays have been experienced during troubleshooting to resolve problems following the installation of the modification. As a result, the 72-hour allowed outage time (A0T) of TS 3.8.1.1 will be exceeded at 1954 Eastern daylight time (EDT) on July 8, 1994, for Unit 1.
Currently, the D/G testing is expected to resume early in the af ternoon of July 8.
TS_ Compliance TS 3.8.1.1, Action a, allows a D/G to be inoperable for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> before proceeding to a shutdown condition. The 72-hour period will expire at 1954 EDT on July 8, 1994.
Final postmodification testing is estimated to be completed at approximately 2300 EDT on July 9.
In order to allow adequate time to complete additional inspection and testing of the 2A-A D/G, 41 hours4.74537e-4 days <br />0.0114 hours <br />6.779101e-5 weeks <br />1.56005e-5 months <br /> are requested in addition to the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided by TS 3.8.1.1 to prevent unit shutdown.
Sately_ Consequences The af fected D/G supplies emergency power f or the following significant common systems that affect Unit 1 operation:
One ERCW pump on the A train header
[
One train of ventilation for the electric board areas and the auxiliary building MDAFW area coolers